In circular knitting machines having a plurality of vertically reciprocable knitting needles arranged in a circle it often is desirable to knit fabrics in which different portions of the fabric are knitted from different types of yarn. Typically, a circular knitting machine will be associated with a plurality of spools of various types of yarns. Each of the yarns is guided to and held in proximity to the circular array of knitting needles by movable yarn feed fingers located outside the needle circle. The end of the yarn is held at a location within the needle circle so that when viewed in plan, the yarn intersects the needle circle. When it is desired to introduce a particular type of yarn into the knitted fabric, the feed finger which guides that particular yarn may be moved from its remote, upper position in which the yarn is above the needles to a lowered position in which the yarn is engaged by the needles thus enabling the yarn to be incorporated into the knitted fabric. When it is no longer desired to employ that yarn in the fabric, the feed finger guiding the yarn is raised to its remote position which withdraws the yarn from further engagement with the knitting needles. Typically, means are provided to cut the yarn after it has been detached from the needles and means are provided to hold the cut end of the yarn to facilitate reintroduction of the yarn into the fabric when desired.
It has been common practice with non-elastic yarns to move the yarn feed finger to the remote position, thus disengaging the yarn from the needle, then drawing the disengaged portion of the yarn across a suction inlet and then cutting the yarn at a location beyond the suction inlet. The suction inlet is connected to a vacuum pump and after the yarn has been cut, its free end is ingested into the suction inlet to hold the free end of the yarn under light tension. The suction inlet and yarn feed finger cooperate to hold the end of the yarn above the needles and the needle circle in readiness to reintroduce the yarn into the fabric. Once the yarn has been re-engaged with the knitting needles operation of the knitting needles easily draws the previously cut end of the yarn out from the suction inlet and to a cutting station where the free end can be severed from the portion of the yarn which has been knitted into the fabric.
It sometimes occurs that the cut end of the yarn is not held properly and this may result in some very serious difficulties. If the cut end of the yarn is not held properly within the needle circle but instead hangs loosely from the yarn feed finger, it will not be in a proper position to be reattached to the needles when the yarn feed finger moves downwardly to the yarn re-engaging position. Continued operation of the machine without proper engagement of the yarn with the needles results in an improperly knit, faulty garment. When this occurs after part of the garment has been knit, all of the yarn used in that part of the garment is wasted. This can be relatively expensive if it happens often enough. In addition, many circular knitting machines have an automatic shut-off feature in which the machine shuts down should the knitting needles miss or not properly engage the yarn. Shutdown of the machine often is a somewhat rapid procedure and because of the delicacy of the needles and some of the other parts of the knitting machine this sometimes results in breakage of some of these parts. This, in turn, results in substantial down time of the machine which also is obviously undesirable.
In general, the vacuum holding technique described above has proved satisfactory for relatively inelastic yarns. The difficulties described above, however, become particularly acute with stretchable elastic yarns of the type used in stretch fabrics such as in panty hose, etc. In order for such stretch garments to have their stretch quality they must be knit with the elastic yarn in a highly tensioned and stretched configuration. This is required so that after the fabric has been knitted, it will contract under its own elasticity so that it may thereafter stretch from its contracted state. Because the yarn is highly stretched during the knitting process, when it is cut it tends to contract and withdraw from the vacuum inlet so that often it cannot be held by the conventional vacuum holding technique described above.
Efforts have been made to solve the above difficulty encountered with the cutting and holding elastic yarns. To this end a special mechanical device has been employed with such yarns which mechanically cuts and grips the yarn. The device does present a number of serious difficulties in that while it is effective to cut the yarn, it does not maintain a reliable grip on the cut end of the yarn. Frequently the cut end of the yarn simply falls loosely about and it cannot be properly reintroduced to the knitting needles when desired which results in the difficulties described above. In addition, yarn waste is a significant factor with stretchable yarns which are considerably more expensive than yarns of the inelastic variety.
It is among the primary objects of the invention to provide an improved attachment to a circular knitting machine which cuts and grips the yarn, is extremely reliable and eliminates the above difficulties.